This application relates to a scroll compressor wherein recesses are formed on a crankcase or rear face of an orbiting scroll.
Scroll compressors are widely utilized in refrigerant compression applications. In a scroll compressor, a first scroll member has a base and a generally spiral wrap extending from the base. A second scroll member also has a base and a generally spiral wrap extending from its base. The wraps of the two scroll members interfit to define entrapped fluid chambers. As second scroll member orbits relative to the first scroll member, the volume of the fluid chambers is reduced. The volume chamber reduction causes the compression of entrapped refrigerant.
As the refrigerant is being compressed, pressure in the compression chambers of the two intermeshing scroll wraps produces an axial force acting on the scroll base that tends to separate the two scroll elements away from each other. To resist this separating force, a so-called back pressure chamber is formed between the crankcase forward face and the rear face of the base of the second scroll member. A compressed refrigerant is tapped into this back pressure chamber. Pressure in this back chamber biases the second scroll member back towards the first scroll member. The back pressure chamber is typically defined and sealed by a pair of radially spaced seals. To accommodate for manufacturing and assembly tolerances as well as thermal and structural deformations, the second scroll member is allowed to have a small axial movement with respect to the crankcase.
As can be appreciated, the second scroll member is carefully positioned relative to the crankcase within tight tolerances. If there is too much gap between the rear of the base of the second scroll member and the forward face of the crankcase, the seal reliability can be jeopardized, as the seals need to seal over a wider then desired gap. On the other hand, if the gap is insufficient, then the second scroll member can lock up on the crankcase surface, which will quickly lead to the compressor damage. Thus, a scroll compressor designer has to carefully select the desired gap, taking into account potential production variation in machining the surfaces of the crankcase and orbiting scroll member. As an example, an applicant has found these variations to be on the order of 40 microns across the base of the orbiting scroll or the crankcase facing surface. For this reason, tight tolerances are required in machining the crankcase surface and the rear surface of the second scroll member to maintain the desired gap. However, tighter tolerances call for higher assembly and manufacturing costs.
The present invention is directed to addressing the above-discussed problem.